Since our denominators match, we can add the numerators.
1 + 3 = 4
The sum we get is
The last step is to reduce the fraction if we can.
To find out, we try dividing it by 2...
Nope. Try the next prime number, 3...
Nope. Try the next prime number, 5...
No good. 5 is larger than 4. So we're done reducing.
Congratulations! Here's your final answer to 1/9 + 3/9